It is a type of Halimeda macroalgae. It grows like crazy at times for me and takes on a bright green, and then it will just sit there for months without growing at all. Right now it is in its growing stage. My wife was just commenting last night about how bright of a green it currently is. With that being said, my actinics were turned off at the time of the pics and the pictures all have a little bit of a yellowish tint to them. The yellowish tint isn't actually there and it is probably washing out the corals colors some and exaggarating the greens.
BTW - Can you tell that the 10 gallon FW tank is setup for my 5yr old? No plants, blue gravel, and a castle.
